Why isn't cubase picking up any signal from my mic?

I recently bought the yamaha audiogram 6 usb interface which came with cubase 5. I also purchased the audio technica AT2050 and have it connected to the interface via an XLR cord. I can hear the mic in my headphones which are plugged into the interface, but cubase won't record anything with it, let alone pick up any sort of signal from it. Any ideas?